Java lambda&Stream

匿名类写法
new Thread(new Runnable(){
	@Override
	public void run(){
	System.out.println("hello");
	}	
}).start();

Lambada写法
new Thread(()->System.out.println("hello")).start();

() -> {}

    ()：接口方法的括号，接口方法如果有参数，也需要写参数。若只有一个参数时，括号可以省略。
    -> : 分割左右部分。
    {} : 要实现的方法体。只有一行代码时，可以不加括号，可以不写return。

package com.lrm.web;

public class Test {
    public static void main(String[] args) {
        //参数声明
        creat((a,b)->a+b);

        //单行语句块：必须要有结果
        creat((a,b)->a+b);

        //多行语句块
        creat((a,b)->{
            System.out.println("1");
            return a+b;
        });

        //静态引用
        creat(Test::staticMethod);//引用Test类下的static_me方法
        //非静态引用
        creat(new Test()::notStatic);
        //工具类方法引用
        creat(String::concat);
    }

    private String notStatic(String name,String message){
        return name+message;
    }

    private static String staticMethod(String name, String message){
        return name+message;
    }

    private static void creat(myInter myInter){
        myInter.build("11","22");
    }

    public interface myInter{
        String build(String name, String message);
    }

}

// 获取所有红色苹果的总重量
appleStore.stream().filter(a -> "red".equals(a.getColor()))
.mapToInt(w -> w.getWeight()).sum()


// 基于颜色统计平均重量
appleStore.stream().collect(Collectors.groupingBy(a -> a.getColor(),
        Collectors.averagingInt(a -> a.getWeight()))).forEach((k, v) -> {
    System.out.println(k + ":" + v);
});

//获取所有红色苹果的总重量
select sum(a.weight) from apple as a  where a.color='red';
// 基于颜色分组统计重量
select a.color,sum(a.weight) from apple as a group by color;

// 获取所有会员ID 并去重
List<Integer> ids = orders.stream().map(o -> o.getMemberId()).distinct().collect(Collectors.toList());
//  合并会员信息 至订单信息
orders.stream().forEach(o -> {
    Member member = members.stream().filter(m -> m.getId() == o.getMemberId()).findAny().get();
    o.setMemberName(member.getName());
});

public void test(){
	appleStore.stream(){
		.peek(a->System.out.println(a.getColor()))//打印颜色
		.peek(a->System.out.println(a.getOrigin()))//打印产地
		.toArray();
}

public void test(){
	for(Apple apple : appleStore){
		System.out.println(a.getColor());//打印颜色
		System.out.println(a.getOrigin());//打印产地
}

 @Test
    public void filterTest() {
        appleStore.stream().filter(a -> a.getColor().equals("red")).forEach(a -> {
            System.out.println(a.getColor());
        });
    }

    @Test
    public void mapTest() {
        appleStore.stream().map(a -> a.getOrigin()).forEach(System.out::println);
    }

    @Test
    public void flatMapTest() throws IOException {
        Stream<String> lines = Files.lines(new File("G:\\git\\tuling-java8\\src\\main\\java\\com\\tuling\\java8\\stream\\bean\\Order.java").toPath());
        lines.flatMap(a -> Arrays.stream(a.split(" "))).forEach(System.out::println);
    }

    @Test
    public void sortedTest() {
        appleStore.stream().sorted((a, b) -> a.getWeight() - b.getWeight())
                .map(a -> a.getWeight()).forEach(System.out::println);
    }

    @Test
    public void peekTest() {
        appleStore.stream().peek(a -> {
            System.out.println(a.getId());
        }).map(a -> a.getOrigin())
                .peek(System.out::println).forEach(a -> {
        });
    }

    @Test
    public void reduceTest() {
        // 找出最重的那个苹果
        appleStore.stream().reduce((a, b) -> a.getWeight() > b.getWeight() ? a : b)
                .ifPresent(a -> {
                    System.out.println(a.getWeight());
                });
    }

    @Test
    public void collectTest() {
        // 将结果转换成id作为key map<Integer,Apple>
        HashMap<Integer, Apple> map = appleStore.stream().collect(HashMap::new, (m, a) -> m.put(a.getId(), a), (m1, m2) -> m1.putAll(m2));
        map.forEach((k, v) -> {
            System.out.println(k);
            System.out.println(v);
        });
        // Map<String,List<Apple>>
        //  基于颜色分组， 并获取其平均重量


    }

 // 获得所有颜色苹果的平均重量
    @Test
public void groupByTest() {
        Collector<Apple, ?, Map<String, Double>> groupCollect =
                Collectors.groupingBy((Apple a) -> a.getColor(), Collectors.averagingInt((Apple a) -> a.getWeight()));
        appleStore.stream().collect(groupCollect).forEach((k, v) -> {
            System.out.println(k + ":" + v);
        });
    }